Conductively coated bushing terminal guard



June 29,1965 w. J. WEINFURT CONDUCTIVELY COATED BUSHING TERMINAL GUARD Filed June 14, 1965 INVENTOR WILLIAM J.WE|NFURT 9M wm ATTORNEY United States Patent 3,192,311 CONDUCTIVELY COATED BUSHING TERMINAL GUARD William J. Weinfurt, Elm Grove, Wis., assignor to McGraw-Edison Company, Milwaukee, Wis., a

corporation of Delaware Filed June 14, 1963, Ser. No. 287,873 3 Claims. (Cl. 174-139) This invention relates to brushing terminal guards and more particularly to a protective cover for the high volt age bushing terminals of electrical apparatus.

It is common for service outages in electrical distribution systems to result from arcovers between the high voltage bushing terminals and the grounded case of pole mounted electrical apparatus, such as transformers, which are caused by birds, squirrels and other small game.

Prior art devices for preventing such outages generally include an insulating cover guard for the high voltage bushing terminals. High voltage terminal guards of this type have not been entirely satisfactory because they .did not discourage small creatures from assuming positions relative to the terminal and the grounded apparatus casing which would tend to initiate flashovers.

It is an object of the invention to provide a new and improved terminal guard which discourages small creatures from assuming a fault initiating position.

Another object of the invention is to provide a bushing terminal guard which causes small creatures to receive an electrical shock to discourage further advancement but which does not cause serious injury.

A more specific object of the invention is to provide a bushing terminal guard consisting of a conductive material which is disposed in a surrounding relation to the bushing terminal but electrically insulated therefrom and from the grounded metallic casing of the electrical apparatus which supports the bushing.

These and other objects and advantages of the instant invention will become more apparent from the detailed description thereof taken with the accompanying drawings in which:

FIG. 1 is a side elevational view, partly in section of the bushing terminal guard according to the instant invention; and

FIG. 2 is a top plan view of the bushing terminal guard shown in FIG. 1.

Referring now to the drawings in greater detail, FIG. 1 shows a bushing suitably aifixed to and extending through the cover 11 of electrical apparatus such as a transformer.

As will be understood by those skilled in the art, a terminal 12 is disposed at the upper end of the bushing 10 and is aflixed to the upper end of a conductive stud (not shown) which extends downwardly through the bushing 10 for connection to the apparatus within the casing 11. The terminal 12 includes a clamping block 14 having a bore 15 extending therethrough in a direction generally transversely to the axis of the bushing 10 and having a plurality of conductor engaging teeth 16 on one face thereof and surrounding said bore.

The terminal also includes a clamp member 17 having an eye 19 provided with a central aperture 20 for receiving the lower end of a conductor 22. In addition, the clamp 17 includes a threaded stud 23 extending from the head 19 and through the bore 15 of the clamp block 14 for engagement by a nut 24.

It will be appreciated that when the nut 24 is tightened the clamp 17 will move towards the right as viewed in FIG. 1 forcing the conductor 22 into high pressure engagement with the teeth 16 of the clamp block 14 to provide a good electrical connection therebetween.

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The terminal guard according to the instant invention includes a hollow tubular member 26 composed of suitable insulating material such as an epoxy-glass composition and is disposed with its lower edge in engagement with the upper skirt of the bushing 10 and in surrounding relation relative to the terminal 12 and the conductor 22. The outer surface of the tube 26 is covered by a metallic coating 27 which may consist of any suitable conductive material such as aluminum paint and which may be applied in any suitable manner such as by spraying or brushing. The conductive metallic coating 27 terminates at 28 below the upper edge of the tubular member 26.

The tube 26 is held in position by a spring member 30 having a flat base portion 31 which is affixed to the clamp block 14 by the nut 24. Spring member 30 also has a pair of curved arms 32 each of which resiliently engages the inner surface of the tubular insulating member 26. A plurality of notches 33 are cut in the lower edge of the tubular insulation member 26 to allow moisture to drain away from the interior thereof.

When the electrical apparatus is energized the conductive coating 27 will acquire a static charge due to the field around the terminal 12 and the conductor 22. The magnitude of the charge will depend on the field voltage gradient and the effective capacitance of the coating. Normally because of the close proximity between the coating 27 and the terminal 12, the potential on the conductive coating 27 will be substantially the same as that on the terminal 12. As a result the electrical stress on the insulating tubing 26 will be relatively low.

Should an animal bridge the gap between the conductive coating and the cover of the apparatus casing 11, the charge from the coating 27 will discharge through the animals body causing an unpleasant sensation and discourage further advance. The charge, however, will not be sufiicient to cause serious injury to the animal. As soon as the animal disengages the conductive coating 27, the latter will immediately acquire another static charge in the event of another encounter.

While only a single embodiment has been shown and described, it is not intended that the invention be limited thereby but only by the scope of the appended claims.

I claim:

1. In combination with an elongate electrical bushing having an insulating body and a conductive clamp on one end thereof for releasably engaging an electrical conductor, a tubular insulating member having a lower edge engaging said insulating body and extending upwardly therefrom in spaced-apart surrounding relation to said conductive clamp, said tubular member having a conductive coating disposed on the outer surface thereof at a point adjacent said conductive clamp and electrically insulated therefrom, said clamp and said conductive coating forming a capacitor whereby the flow of current through said conductive clamp will cause a charge to accumulate on said coating, the capacitive coupling between said clamp and said conductive coating being the sole means of electrical coupling therebetween.

2. In combination with the grounded outer metallic housing of electrical apparatus, an electrical bushing for conducting electrical energy through said outer metallic housing and including an elongate body of insulating material, a conductive clamp mounted at the upper end of said body for connection to an electrical conductor, a hollow tubular insulating member having a lower edge engaging said insulating body and extending upwardly therefrom, resilient means extending between said clamp and the inner surface of said tubular member to hold the latter adjacent said clamp and in spaced relation thereto and to said conductor, said tubular member having a conductive coating disposed on its outer surface at point adjacent said conductive clamp and electrically insulated therefrom, said clamp and said conductive coating forming a capacitor whereby the flow of current through said conductive clamp willcause a charge to accumulate on said coating, the capacitive coupling between 'said clamp and said conductive coating being the sole means of electrical coupling therebetween.

3. In combination with an electrical bushing having an insulating body and a conductive clamp on the upper end thereof for releasably engaging an electrical conductor, an elongate, hollow, open-ended insulating member having a lower edge engaging said insulating body and extending upwardly therefrom in spaced apart surrounding relation to said conductive clamp, said insulating member extending a substantial distance past said conductive clamp and along said conductor, a conductive coating disposed on the outer surface of said insulating member and extending for a substantial portion of its length, said conductive coating being electrically insulated References Cited by the Examiner UNITED STATES PATENTS 1,856,122 5/32 Austin 174142 X 2,834,829 5/58 Broverman 174-5 X 2,840,631 6/58 Marcroft 174-14O 2,875,267 2/59 Sutton 174-139 3,019,287 1/62 Newcomb et a1. 1745 X LARAMIE E. ASKIN, Primary Examiner.

E. JAMES SAX, Examiner. 

1. IN COMBINATION WITH AN ELONGATE ELECTRICAL BUSHING HAVING AN INSULATING BODY AND A CONDUCTIVE CLAMP ON ONE END THEREOF FOR RELEASABLY ENGAGING AN ELECTRICAL CONDUCTOR, A TUBULAR INSULATING MEMBER HAVING A LOWER EDGE ENGAGING SAID INSULATING BODY AND EXTENDING UPWARDLY THEREFROM IN SPACED-APART SURROUNDING RELATION TO SAID CONDUCTIVE CLAMP, SAID TUBULAR MEMBER HAVING A CONDUCTIVE COATING DISPOED ON THE OUTER SURFACE THEREOF AT A POINT ADJACENT SAID CONDUCTIVE CLAMP AND ELECTRICALLY INSULATED THEREFROM, SAID CLAMP AND ELECTRICALLY ING FORMING A CAPACITOR WHEREBY THE FLOW OF CURRENT THROUGH AND SAID CONDUCTIVE CLAMP WILL CAUSE A CHARGE TO ACCUMULATE ON SAID COATING, THE CAPACITIVE COUPLING BETWEEN SAID CLAMP AND SAID CONDUCTIVE COATING BEING THE SOLE MEANS OF ELECTRICAL COUPLING THEREBETWEEN. 